This project focuses on physicochemical properties of nucleic acids as studied mainly by electron microscopy. A major objective is the elucidation of the intimate relationship between conformation of nucleic acid molecules and their biological function in living matter which is exerted by contact with other molecular components. We study conformational changes in isolated deoxyribonucleic acids (DNA) under defined, simple conditions such as various salts of different ionic strengths in the aqueous solvent. It is the guiding hypothesis that the local activity of water in the living cell -- influenced by ions -- is playing an important role. We observe drastic structural changes of DNA into condensed supercoils, upon dehydration by ethanol, resembling chromatin and chromosome condensation in cells. We wish to explore the possibility that histones displace water when binding to DNA thereby inducing supercoiling of the chromosome. Other major efforts aim at physical mapping of functional sites in extrachromosomal bacterial DNA's which carry resistance against antibiotics. This will be done by detection of AT-rich regions along DNA by partial strand separation within the double helix and by means of restriction enzymes cleaving DNA at specific sites. Finally, transcription of adenovirus DNA in cultured mammalian cells will be analysed by electron microscopy of DNA:RNA hybrid molecules.